Not realizing that OS X creates a ~/Sites folder when you enable web sharing, I started putting my sites for MAMP within a ~/Sites directory, which did not exist on my new laptop. Is this ok, as long as I don't enable web sharing? Even if I did enable it, would something happen to the other files I put in there?

Any files you put in the ~/Sites folder will be treated the same way most web hosts treat the files. HTML, images & scripts (scripts may need special changes to htaccess & httpd.conf) will be served normally from http://my-Mac-name-here.local/~jjeaton/ .

So, like a typical webserver, whatever files you put in there will not be changed unless you youself edit/move/delete them.

You should also double check the permissions so that only you have read/write/execute permission and group & others only have read/execute.